Deuteronomy 5:29 (26 in Heb.); 32:29; Psalm 81:13ff. (14ff.); Isaiah 48:18. The purpose of adducing these texts is to note the optative force of that which is expressed. There can be no reasonable question as to the optative force of Deuteronomy 5:29 (26). It is introduced by the idiom mi yitten which literally means “who will give?” but is really a strong optative expression meaning “Oh that there were!” Consequently the text reads, “Oh that there were such a heart in them, that they would fear me, and keep all my commandments always, that it might be well with them, and with their children for ever!” It is the Lord who is speaking and we shall have to conclude that here we have the expression of earnest desire or wish or will that the people of Israel were of a heart to fear him and keep all his commandments always. It is apparent from the book of Deuteronomy itself (cf. 31:24-29) and from the whole history of Israel that they did not have a heart to fear God and to keep all his commandments always. Since they did not fulfil that which was optatively expressed in 5:29 (26), we must conclude that God had not decreed that they should have such a heart. If God had decreed it, it would have been so. Here therefore we have an instance of desire on the part of God for the fulfilment of that which he had not decreed; in other words, a will on the part of God to that which he had not decretively willed.
In Deuteronomy 32:29 the construction is somewhat different. In our English versions it is translated, “Oh that they were wise, that they understood this, that they would consider their latter end.” This rendering is distinctly optative and has the same effect as Deuteronomy 5:29 (26), considered above. It must be admitted that this is a perfectly legitimate rendering and interpretation. The conjunction lu with which the verse begins has undoubtedly this optative force. It has such force unquestionably in Genesis 17:18; Numb. 14:2, 20:3; 22:29; Joshua 7:7; Isaiah 63:19, and possibly, if not probably, in Genesis 23:13, 30:34. When lu has this optative force it means “Oh that” or “if only” and expresses strong desire. In view of what we found in Deut. 5:26 there is no reason why the optative force of lu should not be adopted here. We may not, however, insist that lu must have optative force here because lu is also used with conditional force, as in Judges 8:19; 13:23; II Samuel 18:12 and elsewhere. If lu is understood conditionally, Deut. 32:29 would be rendered as follows: “If they were wise they would understand this, they would consider their latter end.” This, however, is not the most natural rendering. The optative interpretation is smoother and more meaningful in the context. If this more natural construction is followed it shows the same thing as we found in Deut. 5:26, that earnest desire is expressed for what is contrary to fact (cf. v. 28).
In Psalm 81:14 it may readily be detected that the conditional force of the conjunction lu cannot reasonably be adopted. The thought is rather distinctly optative, “Oh that my people were hearkening unto me, that Israel would walk in my ways.”
Isaiah 48:18 could readily be rendered conditionally thus: “If thou hadst hearkened to my commandments, thy peace had been as a river and thy righteousness as the waves of the sea.” It can also be rendered optatively, as in our English versions.
It should be noted that even when the conjunction lu is given very distinct conditional force, the optative idea is sometimes rather noticeably in the background. This would very likely be the case in Isaiah 48:18, even if the optative rendering gives way to the conditional. The desirableness of that which is expressed in the condition and its corresponding consequence cannot be suppressed. This can be expressed in our English idiom very well when we render, “If only thou hadst hearkened to my commandments, then had thy peace been as a river,” etc. Both the conditional and optative appear here, and there is much to be said in favour of the conclusion that whether we render Isa. 48:18 optatively or conditionally the optative notion still persists, in the former case, of course, directly and in the latter case indirectly.
Should we make full allowance for doubt as to the exact force of the construction in the case of Deut. 32:29 and Isa. 48:18, there can be no room for question but that the Lord represents himself in some of these passages as earnestly desiring the fulfilment of something which he had not in the exercise of his sovereign will actually decreed to come to pass. This bears very directly upon the point at issue.
John Murray, The Free Offer of the Gospel,” in The Collected Writings of John Murray (Edinburgh: The Banner of Truth, 1976), 4:117-119.